Ruthenium(II) complexes with phenanthroline-, benzimidazole-, benzothiazole-, and pyridine-derived bidentate and tridentate ligands: reactivity and spectroscopic and electrochemical characterization

Ruthenium complexes of some tridentate and bidentate benzimidazole-, benzothiazole- and pyridine-derived ligands have been prepared as their PF f6 p− salts, and their constitutions have been confirmed by elemental analysis, 1H-n.m.r. spectroscopy and electrochemistry. The complexes are redox-active, displaying a metal-centred RuII/ RuIII oxidation process and sequential ligand-localized reduction processes. Both the 2-(2′-pyridyl)benzimidazole complex [Ru(PybimH)3]2+ and the 2,2′-dipyridylamine one, [Ru(DpyaH)3]2+ behave as weak Bronsted-Lowry acids. The secondary amino nitrogen of each DpyaH in the [Ru(DpyaH)3]2+ complex can be deprotonated with hydride anion, and then acts as a strong nucleophile, allowing selective N-alkylation by alkyl halides. Most of the complexes exhibit ligand-localized luminescence emission at ambient temperature. The strong intrinsic fluorescences of 2-(2′-quinolyl)-N-methylbenzimidazole and 2-(2′-pyridyl)-benzimidazole are quenched when they are coordinated to RuII, and emission from the chelates entailing 5-nitro-1:10-phenanthroline occurs only from the non-nitrated ligands.